Q&A: Strength of Concrete Mix

Life Expectancy of Galvanized Fasteners

Q.Many years ago, a concrete
contractor gave me a recipe for mixing concrete by hand
or machine. It is the only mix I have ever used. Is
there any way to know how strong the mix is? I use 1
part Portland cement, 2 parts clean sand, and 3 parts
clean crushed stone (7/16 inch or 3/4 inch, depending
on the job).

A.Bob Shuldes
responds: The strength of your 1-2-3 mix
should be very good, but will vary somewhat
depending on the water content (water/cement
ratio). If you use 4.5 gallons of water per bag of
cement, the strength will be 5,800 psi; at 5 gal.
per bag, 5,300 psi; at 5.5 gal. per bag, 4,800 psi;
at 6 gal. per bag, 4,300 psi; and at 6.5 gal. per
bag, 3,900 psi.

Bob Shuldes, P.E., is a consulting
engineer at the Portland Cement Association in
Skokie, Ill.